1. Field of the Invention
The present invention relates to an injection system and casting method of a die casting machine method.
2. Description of the Related Art
In a die casting machine, an injection plunger is used to inject a molten metal into a cavity of a die by an injection plunger. The quality of the cast product greatly depends upon the injection speed of the molten metal and the casting pressure (injection pressure). Therefore, it is necessary to suitable control the speed of movement (injection speed) and pressure of the injection cylinder driving the injection plunger. That is, the injection speed and the casting pressure (injection pressure) are controlled in accordance with the state of filling the molten metal between the casting cycles to realize the optimal injection operation.
For example, in a predetermined zone after the start of injection, the injection plunger is made to move by a low injection speed so that the molten metal in the injection sleeve does not enter air. Next, when the front end of the molten metal reaches the inlet of the cavity, the injection speed is switched from low speed to high speed to make the injection plunger move by a high injection speed so as to complete the filling of the molten metal into the cavity before the molten metal cools and solidifies. After the molten metal finishes being filled into the cavity, the casting pressure (injection pressure) is rapidly increased and the molten metal is allowed to solidify while applying pressure to the molten metal in the cavity.
The casting pressure finally output after the injection system injects and fills molten metal into the cavity of the die and increases the casting pressure is usually determined in accordance with the pressure of the pressurized oil supplied from the accumulator. The accumulator includes a piston. A gas chamber is formed at one side of the piston. The gas chamber is for example filled with nitrogen gas or another pressure-accumulating gas whereby the pressure is accumulated. For example, by the input and output of the pressurized oil to and from the gas chamber, the volume of the gas chamber can be changed and the pressure accumulated in the accumulator can be adjusted.
On the other hand, the casting pressure differs in accordance with the product concerned (die). Further, it differs depending on the casting conditions even for the same die. Therefore, if exchanging the dies or changing the casting conditions, it is necessary to adjust the pressure setting of the accumulator in accordance with this. The range of adjustment of the pressure of the accumulator depends on the pressure of the pressure-accumulating gas filled in the gas chamber. Therefore, when the changed casting pressure is outside of the range of adjustment of the pressure of the accumulator, the pressure-accumulating gas filled in the gas chamber has to be discharged or charged. To obtain an accurate casting pressure, it is necessary to calculate the amount of the gas filled in the gas chamber. If the gas filled in the gas chamber leaks, the casting pressure will fluctuate, so it was necessary to calculate the amount of gas frequently. In this way, it was necessary to adjust the pressure of the accumulator due to changes in the casting pressure. This work required time. Further, adjustment of the pressure of the accumulator required the discharge or discharge of the nitrogen gas, so there was also the disadvantage of the higher cost.